Not Applicable
The present invention is directed generally to optical transmission systems. More particularly, the invention is directed toward optical transmission systems including optical amplifiers configured to provide for in-service pump maintenance, replacement, and upgrades.
Digital technology has provided electronic access to vast amounts of information. The increased access has driven demand for faster and higher capacity electronic information processing equipment (computers) and transmission networks and systems to link the processing equipment.
In response to this demand, communications service providers have turned to optical communication systems, which have the capability to provide substantially larger information bandwidth transmission capacities than traditional electrical communication systems. Information can be transported through optical systems in audio, video, data, or other signal formats analogous to electrical systems. Likewise, optical systems can be used in telephone, cable television, LAN, WAN, and MAN systems, as well as other communication systems.
Early optical transmission systems, known as space division multiplex (SDM) systems, transmitted one information signal using a single wavelength in separate waveguides, i.e. fiber optic strand. The transmission capacity of optical systems was increased by time division multiplexing (TDM) multiple low bit rate, information signals into a higher bit rate signals that can be transported on a single optical wavelength. The low bit rate information carried by the TDM optical signal can then be separated from the higher bit rate signal following transmission through the optical system.
The continued growth in traditional communications systems and the emergence of the Internet as a means for accessing data has further accelerated the demand for higher capacity communications networks. Telecommunications service providers, in particular, have looked to wavelength division multiplexing (WDM) to further increase the capacity of their existing systems.
In WDM transmission systems, pluralities of distinct TDM or SDM information signals are carried using electromagnetic waves having different wavelengths in the optical spectrum, i.e., far-UV to far-infrared. The pluralities of information carrying wavelengths are combined into a multiple wavelength WDM optical signal that is transmitted in a single waveguide. In this manner, WDM systems can increase the transmission capacity of existing SDM/TDM systems by a factor equal to the number of wavelengths used in the WDM system.
Optical WDM systems were not initially deployed, in part, because of the high cost of electrical signal regeneration/amplification equipment required to compensate for signal attenuation for each optical wavelength throughout the system. The development of the erbium doped fiber optical amplifier (EDFA) provided a cost effective means to optically regenerate attenuated optical signal wavelengths in the 1550 nm range. In addition, the 1550 nm signal wavelength range coincides with a low loss transmission window in silica based optical fibers, which allowed EDFAs to be spaced further apart than conventional electrical regenerators.
The use of EDFAs essentially eliminated the need for, and the associated costs of, electrical signal regeneration/amplification equipment to compensate for signal attenuation in many systems. The dramatic reduction in the number of electrical regenerators in the systems, made the installation of WDM systems in the remaining electrical regenerators a cost effective means to increase optical network capacity.
The increased capacity of information transmitted in WDM systems has made system downtime increasingly more expensive in terms of lost capacity and revenue. Furthermore, the amount of excess system capacity must be increased accordingly to ensure a continued quality of service to customers in the event of a shutdown in part or all of the optical system.
While EDFAs have contributed greatly to the development of WDM systems, EDFAs are a source of failure that can result in the shutdown of an optical link in the system. More specifically, lasers and other optical sources, used in pump sources to supply optical energy to an erbium doped fiber in an EDFA, have proven to be a common point of failure in optically pumped amplifiers.
A pump source failure generally causes an amplifier and optical link shutdown resulting in lost revenues, degraded service quality, and unscheduled labor costs. Because of the high cost of amplifier shutdowns, pump sources generally include redundant optical sources to improve the reliability of the amplifiers.
The need for and use of redundant optical sources doesreduce the power requirements and cost, as well as increase the reliability, of the optical sources. In various EDFA designs, multiple optical sources are combined and used to pump multiple fiber amplifiers to provide redundancy and to more cost effectively deploy the optical sources. For example, see U.S. Pat. Nos. 4,699,452, 5,039,199, and 5,173,957.
The use of redundant optical sources does not improve the reliability of the optical sources, but only the reliability of the optical amplifier. For example, the failure of an optical source in amplifiers having redundant optical sources will generally not cause an unplanned amplifier shutdown, but will usually require a planned maintenance shutdown to repair or replace the failed optical source. A planned maintenance shutdown allows communications traffic to be rerouted to provide continued service and work scheduled, which greatly reduces the cost of the maintenance. Nonetheless, traffic must still be rerouted and the link taken out of service to repair the failed or degraded pump sources resulting in lost revenue and increased costs.
The provisioning of optical systems and the traffic planning costs associated with rerouting of traffic imposes a substantial financial burden on communications service providers. Rerouting of traffic is a particular concern in optical systems that do not have a highly connected network or significant excess capacity to reroute traffic.
Given the trend of continually increasing communication traffic is not expected to diminish, the need for more reliable, higher capacity optical systems will continue to grow. Thus, it is imperative that optical systems be developed including optical amplifiers with increased reliability to allow the optical systems to be operated in an efficient, cost-effective manner.
The apparatuses and methods of the present invention address the above need for more reliable optical systems and optical amplifiers. Optical systems of the present invention includes at least one optical amplifier having a first pump source configured to supply power to the amplifier via a first pumping path. The first pump source can include one or more optical sources, such as DFB or other lasers, that can provide optical energy in narrow or broad wavelength bands to an amplifying fiber.
A second pumping path is also provided to supply power to the amplifier from a second pump source configured to replace power from the first pump source. The first and second pump sources can be operated to replace power from one pump source with power from the other pump source. A controlled replacement of the power allows amplifier performance characteristics, such as the gain and gain profile, over a signal wavelength range to be maintained during pump source maintenance. In various embodiments, additional pumping paths and pump sources can be provided in the optical amplifier and analogously operated.
The optical amplifier can include various combinations of doped fiber amplifiers, such as EDFAs, and Raman fiber amplifiers in one or more amplifier stages and in concentrated, or lumped, and distributed form. In various embodiments, the first and second pumping path provide optical energy, xe2x80x9cpump powerxe2x80x9d travelling in the same direction in the amplifier. In other embodiments, the pump power in the first and second pumping paths travels in opposite directions in the amplifying fiber. Similarly, the pump power can co-propagate and/or counter-propagate with communication signals being unidirectionally or bidirectionally transmitted in the fiber.
Pump power from the optical sources can be combined using one or more combiners as known in the art and in one or more stages as may be appropriate. In various embodiments, standard and WDM couplers, circulators, dichroic devices, prisms, gratings, and other combiners can be used with or without wavelength selective reflective and transmissive elements, such as Bragg gratings and Fabry-Perot or other filters.
In operation, the second pump source can be removably installed to provide pump power to the optical amplifier via the second pumping path. Once in place, the second pump source can be used to replace the pump power supplied by the first pump source to the amplifier and maintain control over the amplifier performance characteristics. When the power has been reduced to a safe level, the first pump source can be replaced or repaired as required. The replacement of pump power can be performed manually be service personnel, but more desirably would be computer controlled and implemented either locally or remotely depending upon the optical system embodiment.
The first pump source can be replaced with a replacement pump source, which will typically be a replacement first pump source, but can also be an upgraded or other pump source. The pump power provided by the second pump source can be replaced by the replacement pump source and the second pump source can be removed. Alternatively, the amplifier can be designed to operate with the second pump source during normal operation.
Accordingly, the present invention addresses the aforementioned need for more reliable optical systems and amplifiers. The improvement in reliability also provides increasingly flexible and upgradable optical amplifiers with higher availability for use in future optical systems. These advantages and others will become apparent from the following detailed description.